This invention relates to a hydraulic pressure regulator for automatic regulation of hydrostatic converters to a constant pressure with hydraulic remote control.
Hydrostatic transmissions comprising regulated or unregulated hydrogenerators and hydromotors, are characterized by high efficiency, long life, high reliability, small mass and dimensions and above all by the capability for continuous regulation of the transmission ratio. Their advantages are, however, most apparent when automatically regulated. The automatic regulation of a hydrostatic transmission to a constant torque by regulation of a hydrostatic regulating converter on the generator or motor side, and regulation to a constant power by regulation of a hydrostatic regulating converter on the motor side, are the two main regulation schemes employed in hydrostatic transmissions which can be realized by regulation of the transmission pressure. In most applications, particularly where power transmissions handling more than 30 kilowatts are involved, and also in the case of inverse power transmissions, it is advantageous to employ a closed hydrostatic transmission incorporating an auxiliary complementary low pressure hydrogenerator.
Known arrangements for automatically regulating the torque and the power output of hydrostatic converters by regulation of the pressure of the hydrostatic transmission are provided by feeding them liquid directly from the output of the regulating hydrogenerator or employing a special construction of the control cyclinder. These techniques are suitable for regulation to a constant pressure value, but do not enable the required pressure value to be remotely controlled.
A drawback of these known arrangements is that the regulation of the control pressure directly at the output of the regulating hydrogenerator is rather difficult due to the high operating pressures. Another drawback of these arrangements is that they are not functionally compatible with other types of regulation, in which low operating pressure servocylinders for the control of the geometrical liquid volume of converters, and auxiliary low pressure hydrogenerators are used. Another drawback of the prior art arrangements is that they can only adjust a single pressure value and do not provide for remote or programmed adjustment of the required pressure value, which is particularly important where mobile working machines are involved.
Accordingly, it is an object of the present invention to eliminate or at least reduce drawbacks of prior art arrangements, and to provide a hydraulic pressure regulator for automatic regulation of hydrostatic converters to a chosen constant pressure. It is another object of the invention to provide an arrangement which facilitates remote control of the hydraulic pressure.
As herein described, there is provided an arrangement for automatically controlling hydraulic pressure, comprising: a hydraulic pressure regulator, a pressure regulator having an inlet and outlet pressure conduit, a servocylinder coupled to said regulator and having a control piston to control the fluid volume thereof, a slide valve having an inlet conduit and a piston, first and second outlet conduits, a control cylinder having a control pressure inlet and outlet, a piston within said control cylinder connected to the piston of said slide valve, a spring within said control cylinder acting on said piston thereof in one direction, a plunger connected to said control cylinder piston, a double acting return valve connected between the inlet and outlet pressure conduits of the pressure regulator, said valve controlling via a pressure conduit the position of said plunger, the first and second outlet conduits of the slide valve being connected to the servocyinder of the pressure regulator.
An advantage of the circuit arrangement of the hydraulic pressure regulator according to the present invention is that it is relatively simple and not demanding in dimensions and manufacture. The invention is particularly suitable for use in hydrostatic transmissions utilizing an auxiliary complementary hydrogenerator as the pressure source. The invention enables the unification of the regulator design with other regulating arrangements, and provides for remote or programmed adjustment of the required pressure to enable realization of a fully automated hydrostatic transmission with a regulating converter on the motor side, particularly for application at mobile working machines.
The regulator of the present invention does not employ mechanical position feedback, but rather utilizes hydraulic dynamic feedback from the outlet pressure drop.